Moisture-crosslinkable polyurethane adhesive for hygiene

ABSTRACT

The invention relates to a moisture-crosslinkable polyurethane adhesive which comprises:  
     a) 70 to 95% by weight of a polyurethane prepolymer obtained by polyaddition of polyols to diisocyanates trimerized as isocyanurates and,  
     b) 5 to 30% by weight of an essentially amorphous poly-a-olefin,  
     the content of free NCO groups representing 1 to 20% by weight of the adhesive.  
     The adhesive according to the invention is used for the adhesive bonding of fixing components of the Velcro® type to articles intended for hygiene.

[0001] The invention relates to a moisture-crosslinkable polyurethaneadhesive which can be used in particular in the field of hygiene.

[0002] It is now commonplace to use fixing systems of the VELCRO® typeto prepare disposable articles relating to the field of hygiene, inparticular nappies for babies or incontinent adults and feminine hygienearticles. It is well known that the systems of the abovementioned typecontain two components: a first component composed of a multitude offine hooks and a second component composed of a multitude of fine loops.By simply pressing on the superimposed components, the hooks are made toenter the loops, which makes it possible to obtain a solid assembly. Thebonding between the two components can be broken by the application of asufficient force. The two components can be assembled and separatedseveral times without a significant decrease in the strength of theassembly.

[0003] In the specific case of disposable nappies, these fixing systemsare arranged on the rear and front parts forming the belt of the nappywhen it is worn by the user (see U.S. Pat. No. 5,176,670).

[0004] The component containing the loops is fixed to the front part ofthe nappy, the loops being directed outwards. This component isgenerally composed of a thin material based on polyolefin fibres or onother synthetic fibres, in particular a knitted fabric (also known astextile mesh). The component is generally provided in the form of astrip of variable size, optionally decorated with patterns, which isadhesively bonded to the outer covering of the nappy. This covering canconsist of a film which is impermeable to liquids, for example apolyethylene or polypropylene film, or of a non-woven which isimpermeable to liquids and permeable to vapour.

[0005] The adhesive bonding of the component containing the loops to theimpermeable material can be carried out by means of thermoplasticadhesives of the polyolefin or urethane type (see CA-A 2,122,942) or ofmoisture-crosslinkable polyurethane adhesives.

[0006] The adhesive bonding is carried out industrially at a high rate,that is to say at a speed which can exceed 150 metres per minute. Theadhesive-bonding devices operate by coating the impermeable materialwith the liquid adhesive and laminating the component containing theloops. The assembly, thus formed, is subsequently subjected tocalendering and to winding off.

[0007] The amount of adhesive deposited must be carefully controlled: anamount which is too low does not make possible satisfactory adhesivebonding and an amount which is too high passes through the pores of thelaminated component, with the risk of spreading over the loops, which isharmful to the fixing of the component containing the hooks.

[0008] It is economically advantageous to seek to limit the amount ofadhesive while maintaining the performance of the adhesive bonding. Tothis end, the Applicant Company has sought to deposit the adhesive onthe component containing the loops.

[0009] Under the abovementioned industrial conditions, the adhesives ofthe prior art have a tendency very quickly to no longer adhere to thecomponent, which results in the adhesive wicking up on the dispensingdevice and the production line shutting down.

[0010] As regards adhesives based on moisture-crosslinkablepolyurethanes, an additional constraint is imposed by the level ofresidual isocyanate monomer, which must be as low as possible forobvious toxicity reasons.

[0011] The Applicant Company has now found a novel adhesive which makesit possible to overcome these difficulties.

[0012] The invention relates to a moisture-crosslinkable polyurethaneadhesive which comprises:

[0013] a) 70 to 95% by weight of a polyurethane prepolymer obtained bypolyaddition of at least one polyol to at least one diisocyanatetrimerized as isocyanurate and,

[0014] b) 5 to 30% by weight of an essentially amorphous poly-a-olefin,the content of free NCO groups representing 1 to 20% by weight of theadhesive.

[0015] The moisture-crosslinkable polyurethane adhesive preferablycomprises:

[0016] a) 85 to 95% by weight of a polyurethane prepolymer obtained bypolyaddition of at least one polyol to at least one diisocyanatetrimerized as isocyanurate and,

[0017] b) 5 to 15% by weight of an essentially amorphous polyolefin, thecontent of free NCO groups representing 1 to 10% by weight of theadhesive.

[0018] The polyol participating in the formation of the prepolymer isgenerally chosen from polyether polyols, polyester polyols andunsaturated polyols.

[0019] The polyether polyols are generally chosen from aliphatic andaromatic polyether polyols and mixtures of these compounds. Theiraverage molecular mass is preferably between 200 and 9000 and theirhydroxyl functionality is preferably between 2 and 4.6.

[0020] Mention may be made, as examples of aliphatic polyether polyols,of oxyalkylated derivatives of diols, such as polypropylene glycols, orof triols, such as glycerol, trimethylolpropane and hexane-1,2,6-triol,polymers of ethylene, propylene or butylene oxide, copolymers ofethylene oxide and of propylene oxide, the above-mentioned compoundscontaining silanyl endings, and oxyalkylated diphenyl derivatives, suchas derivatives oxyethylenated or oxypropylenated in the 4,4′-position ofdiphenylmethane.

[0021] Use is preferably made of oxypropylated derivatives of glycerol,polymers of propylene or butylene oxide, and copolymers of ethyleneoxide and of propylene oxide.

[0022] The polyester polyols are generally chosen from aliphatic andaromatic polyester polyols and mixtures of these compounds. Theiraverage molecular mass is preferably between 250 and 7000 and theirhydroxyl functionality is preferably between 2 and 3.

[0023] Mention may be made, by way of examples, of the polyester polyolsresulting from the condensation of aliphatic, cyclic or aromaticpolyols, such as ethanediol, 1,2-propanediol, 1,3-propanediol, glycerol,trimethylolpropane, 1,6-hexanediol, 1,2,6-hexanetriol, butenediol,sucrose, glucose, sorbitol, pentaerythritol, mannitol, triethanolamine,N-methyidimethanolamine and mixtures of these compounds, with an acid,such as 1,6-hexanedioic acid, dodecanedioic acid, azelaic acid, sebacicacid, adipic acid, 1,18-octadecanedioic acid, phthalic acid, succinicacid and mixtures of these acids, an unsaturated anhydride, such asmaleic or phthalic anhydride, or a lactone, such as caprolactone.

[0024] Use is preferably made of the polyester polyols resulting fromthe condensation of ethanediol, 1,3-propanediol and/or 1,6-hexanediolwith adipic acid and/or phthalic acid.

[0025] The unsaturated polyols are generally chosen from polyols andmixtures of polyols preferably having a molecular mass of between 1200and 3000.

[0026] Mention may be made, by way of examples, of polybutadiene andpolyisoprene containing hydroxylated endings.

[0027] The abovementioned polyols are advantageously amorphous.

[0028] The abovementioned polyols can also be used as a mixture withother hydroxylated compounds.

[0029] It is thus possible to use a monol or a mixture of monols, inparticular poly(ethylene/butylene)monols, such as Kraton Liquid™ L-1203Polymer, sold by Shell, or a polyol or a mixture of polyols chosen frompoly(ethylene/butylene)diols, such as Kraton Liquid™ Polymer HPVM-2203,sold by Shell, copolymers of ethylene, of vinyl acetate and of2-hydroxyethyl acrylate, such as Orevac® 9402, sold by Elf Atochem,indene/coumarone resins modified by phenol, for example Novares CA120,sold by VFT, and hydroxylated tackifying resins, for example Reagem,sold by DRT.

[0030] The abovementioned monol and the abovementioned polyolrespectively represent 0 to 10% and 0 to 25% by weight of the polyols.

[0031] The diisocyanate trimerized as isocyanurate derives fromdiisocyanates chosen from the group composed of diphenylmethane4,4′-diisocyanate, diphenylmethane 2,4′-diisocyanate and hydrogenationproducts of the abovementioned diisocyanates, toluylene2,4-diisocyanate, toluylene 2,6-diisocyanate, hexamethylenediisocyanate, isophorone diisocyanate and naphthylene 1,5-diisocyanateand their mixtures.

[0032] A trimerized hexamethylene diisocyanate or a trimerizedisophorone diisocyanate is preferred.

[0033] The diisocyanate trimerized as isocyanurate generally containsless than 0.2% by weight of free isocyanate monomers.

[0034] The polyurethane prepolymer is obtained by polyaddition of atleast one polyol and of at least one diisocyanate trimerized asisocyanurate in amounts such that the content of isocyanate groups inthe prepolymer is between 1 and 25% and preferably between 2 and 15% byweight.

[0035] The nature of the polyurethane prepolymer is capable ofinfluencing the hardness of the adhesive according to the invention. Inthis respect, preference is given to the polyurethane prepolymersobtained by reaction:

[0036] of a mixture of polyols composed:

[0037] x of 20 to 100% by weight of an aliphatic polyester polyol,

[0038] x and of 0 to 80% by weight of an aliphatic/aromatic polyesterpolyol

[0039] and of at least one diisocyanate trimerized as isocyanurate.

[0040] Preference is particularly given to the polyurethane prepolymersobtained by reaction:

[0041] of a mixture of polyols composed:

[0042] x of 30 to 50% by weight of an aliphatic polyester polyol,

[0043] x and of 70 to 50% by weight of an aliphatic/aromatic polyesterpolyol

[0044] and of at least one diisocyanate trimerized as isocyanurate.

[0045] The essentially amorphous poly-a-olefin (APAO) is generallychosen from polymers resulting from the copolymerization of monomerschosen from ethylene, propene, 1-butene and 1-hexene in the presence ofa catalyst of Ziegler-Natta type and mixtures of these copolymers.Mention may be made, by way of examples, of Vestoplast®, in particularreferenced 508, sold by Huls, Eastoflex®, sold by Eastman Chemical, andRextac®, sold by Rexen. Preference is given to copolymers having amolecular mass of between 7300 and 23,800 and a glass transitiontemperature of between −27 and −36° C. Use is advantageously made ofcopolymers having-a ring-and-ball softening point (DIN Standard 52011)of between 80 and 160° C.

[0046] The moisture-crosslinkable adhesives according to the inventioncan comprise conventional additives known to a person skilled in theart, such as fillers, tackifying agents, plasticizers, adhesionpromoters, such as compounds containing silanyl groups, and catalystswhich accelerate the crosslinking by moisture, for example metalcatalysts, such as dibutyltin dilaurate, or amine-containing catalysts,such as dimorpholinodiethyl ether.

[0047] The moisture-crosslinkable polyurethane adhesives according tothe invention can be prepared by reacting the polyols and, ifappropriate, the other hydroxylated compounds, optionally dehydrated athigh temperature under vacuum, with the isocyanurates with the exclusionof moisture and, if appropriate, under a protective gas, at atemperature which can vary from 90 to 120° C. After the initiation ofthe reaction, the poly-a-olefin is added, by mixing, in the desiredquantitative ratios and the reaction is allowed to continue until thedesired NCO content is obtained. The optional additives are added, bymixing, to the adhesive thus obtained.

[0048] The moisture-crosslinkable polyurethane adhesives according tothe invention are particularly suited to the industrial adhesive bondingof textile meshes, for example made of cellulose, of polyamide or ofpoly(ethylene terephthalate), and of plastic films, for example made ofpolyethylene, of polypropylene or of poly(ethylene terephthalate). Thisindustrial adhesive bonding is generally employed at a high rate, thatis to say with a speed of progression of the mesh which can exceed 150metres per minute, or indeed more.

[0049] The adhesives according to the invention additionally exhibit acontent of free isocyanate monomer of less than 0.15% by weight of theadhesive, a low vapour pressure at the temperature of use (100 to 130°C.) and consequently a limited toxic nature, an excellent trapping power(ability of adhesive to fix a material) and a good elasticity aftercrosslinking by moisture.

[0050] The following examples allow the invention to be illustrated.

EXAMPLE 1

[0051] The following compounds are introduced into a reactor under anitrogen atmosphere:

[0052] 29.1 parts by weight of hexamethylene diisocyanate isocyanurate(NCO content: 21.6±0.3%; Brookfield viscosity: 3250±750 mPa×s at 23° C.;free hexamethylene diisocyanate: <0.2% by weight; trade name: Desmodur®N3300-Bayer),

[0053] 21.95 parts by weight of the condensation product of adipic acidand of a mixture of 2,2-dimethyl-1,3-propanediol, 1,2-ethanediol and1,6-hexanediol (aliphatic polyester polyol; hydroxyl number: 18-24;molecular mass: 5000; OH functionality: 2; trade name: Dynacoll®7250-Hüls),

[0054] 38.95 parts by weight of the condensation product of a mixture of1,3-benzenedicarboxylic acid and adipic acid and of a mixture of1,4-benzenedicarboxylate, 2,2-dimethyl-1,3-propanediol, 1,2-ethanedioland 3-hydroxy-2,2-dimethylpropyl 3-hydroxy-2,2-dimethylpropanoate(aliphatic/aromatic polyester polyol; hydroxyl number: 31-39; molecularmass: 3000; OH functionality: 2; trade name: Dynacoll® 7130-Hüls).

[0055] The mixture is brought to a temperature of the order of 95 to100° C. When the temperature is stable, 10 parts by weight of copolymerof ethylene, of 1-propene and of 1-butene (molecular mass: 11,800; glasstransition temperature: −31° C.; viscosity at 190° C.: 7800 mPa×s;ring-and-ball softening point (DIN Standard 52011): 86° C.; trade name:Vestoplast® 508-Hüls) are introduced into the reactor.

[0056] After completion of the reaction, 0.01 part by weight ofdibutyltin dilaurate (DBTL) is introduced. A white adhesive is recoveredwhich is solid at 23° C. and which has an NCO content equal to 4.9%,measured according to AFNOR Standard T52-132.

[0057] At 130° C., the adhesive is a white liquid which exhibits astrong tackiness and a Brookfield viscosity equal to 23,000 mPa×s. Oncooling, the adhesive exhibits high elasticity.

[0058] The mechanical properties of the adhesive obtained are defined bythe tensile strength and the elongation at break, measured under theconditions herein-below.

[0059] The molten adhesive is poured at 100° C. onto silicone paperusing a film drawer preheated to 100° C., in order to form a film with alength of 25 cm, a width of 9 cm and a thickness of 300 mm. The film issubjected to a temperature of 23° C. and a relative humidity of 50%until polymerization is complete (of the order of 4 weeks).

[0060] After having removed the silicone paper, the film is cut up witha hollow punch in order to form test specimens (H2 type-AFNOR StandardT46002), which are subjected to tension with a test machine (DY 30 type;Adamel-L'Homargy) at a constant rate of 100 mm/min. The measurements arecarried out on 5 test specimens. Tensile strength:  20 ± 3 MPaElongation at break: 110 ± 15%

[0061] The adhesive-bonding characteristics of the adhesive are definedby the value of the peeling, measured under the following conditions:

[0062] a-Preparation of the Test Specimens

[0063] Test specimens 290 mm long and 100 mm wide are cut out from aflexible polyethylene film containing decorative patterns and apolyamide textile mesh (25 g/m²).

[0064] The polyamide mesh test specimen is fixed to cardboard usingstaples (side with the small loops in contact with the cardboard), inorder to facilitate subsequent handling thereof.

[0065] b-Evaluation of the Adhesive Bonding

[0066] The molten adhesive (100° C.) is poured onto a sheet of glassplaced on a heating plate at 130° C. A film with a thickness of 50 mm(weight per unit area: approximately 5 g/m²), with a length of 25 cm andwith a width of 9 cm is formed using a film drawer preheated to 130° C.and the textile mesh is applied to this film. A slight pressure isexerted on the film and the assembly is removed from the sheet of glassand applied to the polyethylene test specimen, the face containing thepatterns being in contact with the adhesive.

[0067] The assembly is placed in a press in a controlled-environmentchamber at 23° C. and 50% relative humidity for 24 hours, it is thenremoved from the press and polymerization is allowed to proceed tocompletion under the abovementioned temperature and humidity conditions(of the order of 4 weeks).

[0068] The assembly is cut into strips with a width of 25 mm, thecardboard is removed and the outer polyethylene face is reinforced withan adhesive tape. The strips obtained are subjected to a 1800 peeltension at a constant rate of 500 mm/min (Type DY 30 test machine;Adamel-L'Homargy). The measurements are carried out on 5 strips.

[0069] The peel strength is equal to 5 N/25 mm.

[0070] The adhesive is used for carrying out the industrial laminationof a polyethylene film on a polyamide textile mesh (20 g/m²). The moltenadhesive at 110° C. is deposited by means of a lip nozzle on the textilemesh which progresses at the rate greater than 150 metres per minute.

[0071] It is found that there exists no wicking up of the adhesive onthe nozzle and that the wetting of the mesh by the adhesive issatisfactory. It is also observed that the adhesive does not passthrough the textile mesh.

EXAMPLE 2 Comparative

[0072] The preparation is carried out under the conditions of Example 1,modified in that use is made of 30 parts by weight of Desmodur® N3300,25 parts by weight of Dynacoll® 7250, 45 parts by weight of Dynacoll®7130 and 0.01 part by weight of DBTL, and in the absence of Vestoplast®508.

[0073] A white adhesive is recovered which is solid at 23° C. and whichhas an NCO content equal to 5.04%.

[0074] At 130° C., the adhesive is a white liquid, with a Brookfieldviscosity equal to 25,800 mPa×s, which does not exhibit tackiness. Oncooling, the adhesive exhibits high elasticity.

[0075] It is observed that the product wicks up on the nozzle and thatwetting of the textile mesh by the adhesive is absent when the rate ofprogression of the textile mesh is greater than 10 metres per minute.

EXAMPLE 3

[0076] The following compounds are introduced into a reactor under anitrogen atmosphere:

[0077] 25.7 parts by weight of hexamethylene diisocyanate isocyanurate(NCO content: 21.6±0.3%; Brookfield viscosity: 3250±750 mPa×s at 23° C.;free hexamethylene diisocyanate: <0.2% by weight; trade name: Desmodur®N3300-Bayer),

[0078] 34.1 parts by weight of the condensation product of a mixture of1,3-benzenedicarboxylic acid and adipic acid and of a mixture of1,4-benzenedicarboxylate, 2,2-dimethyl-1,3-propanediol, 1,2-ethanedioland 3-hydroxy-2,2-dimethylpropyl 3-hydroxy-2,2-dimethylpropanoate(aliphatic/aromatic polyester polyol; hydroxyl number: 31-39; molecularmass: 3000; OH functionality: 2; trade name: Dynacoll® 7130-Hüls),

[0079] 34.1 parts by weight of a copolymer of ethylene oxide andpropylene oxide (polyether polyol; molecular mass: 3800; OHfunctionality: 2; trade name: Voranol® EP 1900-DOW CHEMICALS),

[0080] 0.004 part by weight of an organobismuth compound (trade name:Coscat® 83-CAMBREX COMPANY).

[0081] The mixture is brought to a temperature of the order of 85 to 90°C. After 2 hours of reaction, 6 parts by weight of copolymer ofethylene, of 1-propene and of 1-butene (molecular mass: 11,800; glasstransition temperature: −31° C.; viscosity at 190° C.: 7800 mPa×s;ring-and-ball softening point (DIN Standard 52011): 86° C.; trade name:Vestoplast® 508-Hüls) are introduced into the reactor.

[0082] After completion of the reaction, a white adhesive is recoveredwhich is solid at 23° C. and which has an NCO content equal to 3.9%,measured according to AFNOR Standard T52-132.

[0083] At 110° C., the adhesive is a white homogeneous liquid, whichexhibits a strong tackiness and a Brookfield viscosity equal to 66,000mPas. On cooling, the adhesive exhibits high elasticity.

[0084] The adhesive is used for carrying out the industrial laminationof a polyethylene film on a polyamide textile mesh in the conditionsdescribed at Example 1.

[0085] It is found that there exists no wicking up of the adhesive onthe nozzle and that the wetting of the mesh by the adhesive isexcellent.

1. Moisture-crosslinkable polyurethane adhesive, characterized in thatit comprises: a) 70 to 95% by weight of a polyurethane prepolymerobtained by polyaddition of at least one polyol to at least onediisocyanate trimerized as isocyanurate and, b) 5 to 30% by weight of anessentially amorphous poly-a-olefin, the content of free NCO groupsrepresenting 1 to 20% by weight of the adhesive.
 2. Adhesive accordingto claim 1, characterized in that it comprises: a) 85 to 95% by weightof a polyurethane prepolymer obtained by polyaddition of at least onepolyol to at least one diisocyanate trimerized as isocyanurate and, b) 5to 15% by weight of an essentially amorphous polyolefin, the content offree NCO groups representing 1 to 10% by weight of the adhesive. 3.Adhesive according to claim 1 or 2, characterized in that thepoly-a-olefin is chosen from polymers resulting from thecopolymerization of monomers chosen from ethylene, propene, 1-butene and1-hexene in the presence of a catalyst of Ziegler-Natta type andmixtures of these copolymers.
 4. Adhesive according to claim 3,characterized in that the poly-a-olefin has a molecular mass of between7300 and 23,800 and a glass transition temperature of between −27° C.and −36° C.
 5. Adhesive according to one of claims 1 to 4, characterizedin that the polyol is chosen from polyether polyols, polyester polyolsand unsaturated polyols.
 6. Adhesive according to claim 5, characterizedin that the polyol is chosen from polyester polyols having an averagemolecular mass of between 250 and 7000 and an OH functionality ofbetween 2 and
 3. 7. Adhesive according to claim 6, characterized in thatthe polyester polyols result from the condensation of polyols chosenfrom ethanediol, 1,2-propanediol, 1,3-propanediol, glycerol,trimethylolpropane, 1,6-hexanediol, 1,2,6-hexanetriol, butenediol,sucrose, glucose, sorbitol, pentaerythritol, mannitol, triethanolamine,N-methyldimethanolamine and mixtures of these compounds with an acid,such as 1,6-hexanedioic acid, dodecanedioic acid, azelaic acid, sebacicacid, adipic acid, 1,18-octadecanedioic acid, phthalic acid, succinicacid and mixtures of these acids, an unsaturated anhydride, such asmaleic or phthalic anhydride, or a lactone, such as caprolactone. 8.Adhesive according to claim 7, characterized in that the polyesterpolyols result from the condensation of ethanediol, 1,3-propanedioland/or 1,6-hexanediol with adipic acid and/or phthalic acid.
 9. Adhesiveaccording to one of claims 1 to 8, characterized in that thediisocyanate trimerized as isocyanurate derives from diisocyanateschosen from the group composed of diphenylmethane 4,4′-diisocyanate,diphenylmethane 2,4′-diisocyanate and hydrogenation products of theabovementioned diisocyanates, toluylene 2,4-diisocyanate, toluylene2,6-diisocyanate, hexamethylene diisocyanate, isophorone diisocyanateand naphthylene 1,5-diisocyanate and their mixtures.
 10. Adhesiveaccording to claim 9, characterized in that the diisocyanate trimerizedas isocyanurate is trimerized hexamethylene diisocyanate or trimerizedisophorone diisocyanate.
 11. Adhesive according to one of claims 1 to10, characterized in that the polyurethane prepolymer is obtained byreaction: of a mixture of polyols composed: x of 20 to 100% by weight ofan aliphatic polyester polyol, x and of 0 to 80% by weight of analiphatic/aromatic polyester polyol and of at least one diisocyanatetrimerized as isocyanurate.
 12. Adhesive according to one of claims 1 to11, characterized in that the polyurethane prepolymer is obtained byreaction: of a mixture of polyols composed: x of 30 to 50% by weight ofan aliphatic polyester polyol, x and of 70 to 50% by weight of analiphatic/aromatic polyester polyol and of at least one diisocyanatetrimerized as isocyanurate.
 13. Use of the adhesive according to one ofclaims 1 to 12 for the adhesive bonding of a fixing component which isprovided in the form of a textile mesh containing a multitude of fineloops and of a plastic film.
 14. Use according to claim 13,characterized in that the textile mesh is made of cellulose, ofpolyamide or of poly(ethylene terephthalate).
 15. Use according toeither of claims 13 and 14, characterized in that the plastic film is afilm made of polyethylene, polypropylene or poly(ethyleneterephthalate).
 16. Article intended for hygiene containing a fixingcomponent in the form of a textile mesh adhesively bonded by means ofthe adhesive according to one of claims 1 to 12.